HI Im New and have a question

Take a look on ebay. I bought an Axis unit there and there are others (brand new) as well. For under $400 you can get a 4 channel DVR with inputs, motion detection and a good size hard drive as well as internet access. The rest of your budget will get you the cameras. I prefer this solution to using a PC as it's stand alone and rock solid reliable.

How are the camers powered? can they be powered fro the usb port ? Separate 110V, battery ?

That varies by camera. Most use a "wall wart" 12 volt regulated power supply. You can get a larger power supply and distribute power from a central location using a combo cable or power them locally.

So there is no way to power them via the usb port they are connected to ?

Some cameras, typically webcams that mount on your monitor, are USB powered. Better cameras that you'd use outdoors are typically 12volt and have a video cable.

USB is a desktop solution. It is for desktop peripherals, not for powering outdoor cameras.

Multicamera systems do no use USB. In fact, most USB camera drivers have problems if more than one camera tries to use the same driver (ie. so your cameras would have to be different manufacturers or models). So that means either using a dedicated multichannel DVR or PCI card and a computer.

There are also IP cameras (and the wireless IP ones), but their capture ability and resolution suck unless you're going to pay $$$ per camera (plus the software needed to manage a multi-camera setup).

Don't bother with wireless analog cameras, they are a joke unless you buy professional tranceivers or are only sending about 20 feet and don't have a cordless phone or wireless network.

Anyway, you don't really say what your price range is or what capabilities you're looking for, so here's something super cheap (watch for URL wrap):